Field of Invention
The present invention relates to a power converter, and more specifically relates to a method and a circuit for detecting attachment of the portable device to the power converter and detachment of the portable device from the power converter.
Description of the Related Art
In the past few years, portable devices (PD) are becoming a necessity to people's lives. Power converters (chargers) designed for those devices usually come with them in the same sales package provided by the manufacturer. This guarantees those portable devices to be always powered under their regulated power-supply specifications.
In recent developments, more and more chargers using USB (Universal Series Bus) cables to connect with their target portable devices are replacing traditional twisted-pair-cable chargers. In addition to those two twisted wires which function the same as the traditional chargers to serve as power supply and ground, there are two additional data lines in USB cables to define the types of charging devices such as SDP (Standard Downstream Port), CDP (Charging Downstream Port) and DCP (Dedicated Charging Port). These two data lines, recently, have been used for communication between the portable devices and the chargers, for example, to adaptively change the power supply level of the chargers by the requests from the portable devices.
The U.S. Patent Application Publication No. 2010/0052620 A1 provides a battery charger IC including built-in USB detection, as shown in FIG. 1A and FIG. 1B. It determines whether the input voltage source comprises the USB voltage or the non-USB voltage using the data pins. Nevertheless, it can't confirm the detachment of the portable device from the charger. Therefore, a method and a circuit for detecting detachment of the portable device from the charger is desired by the industries.